The present invention relates to apparatus constituting a source of laser radiation for use in medical and dental treatments, and to treatment methods which can be performed with such apparatus.
Laser radiation is currently employed in medicine and dentistry for performing a variety of procedures, including procedures which involve cutting, or vaporizing, soft tissues. Specifically, devices known as laser scalpels or laser knives have found acceptance in place of conventional scalpels.
It is also known that laser radiation can be employed to promote healing, and to effect cauterization, coagulation and sterilization among others.
In addition, considerable research has demonstrated the ability of laser radiation having a suitable wavelength and energy density to cut hard tissues, including bone, enamel, dentin and cementum, as well as demineralized hard tissue such as carious tooth tissue. In dental applications, soft tissue which can be cut includes gum, nerve tissue and pulp. Laser radiation can also be employed to cut tartar, plaque or calculus which forms on tooth surfaces, as well as similar materials which accumulate in body passages, including blood vessels and urinary passages.
The term "cutting" used herein encompasses mechanisms such as vaporization, which may be achieved by photoablation, or photodisruption.
The effect of laser radiation on any particular tissue depends essentially on the wavelength and power level of the radiation and the form in which the radiation is delivered, i.e. continuous-wave (CW) or pulsed. Heretofore, it has been the practice, when seeking to perform a particular procedure, whether clinically or in connection with research, to seek the type of laser whose wavelength will be most effective for that procedure, and to then seek to arrive at optimum values for power level and, if pulsed radiation appears preferable, the optimum values for pulse duration and repetition rate. The energy delivered by each such pulse will be a product of the laser power output and the pulse duration. The energy density with which each pulse is applied to tissue being treated will depend on the diameter of the radiation spot on the tissue and is a significant parameter in determining the effect of such laser radiation.
In procedures of the type described above, the ability to apply the radiation to a desired location is of substantial importance and it is known to be desirable to apply the radiation by means of a handpiece which can be easily directed by the physician or dentist. Since, however, lasers themselves, particularly those which must produce the power levels required by such medical treatments, are relatively bulky devices, a handpiece is usable only if a feasible means exists for conducting laser radiation from the laser itself to the handpiece. Optical fibers represent a logical and attractive solution to this problem. However, radiation produced by many of the lasers which are currently in use cannot be satisfactorily transmitted via optical fibers. This is true, for example, for CO.sub.2 laser radiation.
On the other hand, it is known that radiation wavelengths from about 0.5.mu. at least up to about 3.mu. can be efficiently transmitted via conventional optical fibers, at least at relatively low power levels.
Laser radiation having a wavelength of less than 3.mu. includes those produced by the Nd:YAG laser (fundamental wavelength 1.06.mu.) and the Er:YAG laser (fundamental wavelength of 2.94.mu.). Both of these forms of laser radiation are capable of cutting various types of tissue, although each employs a somewhat different mechanism to do so. This difference results in part from the fact that water has a very low coefficient of absorption for radiation at the wavelength of 1.06.mu. and a relatively high absorption coefficient for radiation at the wavelength of 2.94.mu..
U.S. Pat. Nos. 4,931,053 and 4,951,663, to L'Esperance, Jr., disclose apparatus including two lasers producing beams which are aligned onto a common output axis. The laser radiation is selected to avoid inducing photocoagulation, photonoptical tissue breakdown, photovaporization, or photoablative decomposition of the affected body tissue or cells.
According to U.S. Pat. No. 4,931,053, the radiation is selected to enhance vascular or like growth beyond what may be achieved by a single laser.
According to U.S. Pat. No. 4,951,663, the laser radiation is selected to provide a biomedical sterilization system which can destroy microorganisms in the dermis as well as in the epidermis.
U.S. Pat. No. 4,925,523, to Braren et al, discloses apparatus in which beams of laser radiation at the wavelengths of 193 nm and 308 nm are aligned on a common output axis and are applied to a workpiece to produce an enhanced ablative effect. The 193 nm radiation excites molecules of the workpiece material to cause some of the molecules to ablate and others to enter the triplet state without ablating. The 308 nm wavelength ablates molecules which have been placed in the triplet state. The 308 nm wavelength can not itself ablate molecules which have not been excited. This patent mentions other wavelength pairs, describes the effect of the radiation on various plastic materials, and hypothesizes that the method can be used to etch organic substrates including tissue, bone and teeth.
U.S. Pat. No. 4,408,602, to Nakajima, discloses a system having two laser cutting sources each of which is effective on different types of tissues, means being provided to switch between sources.